1. Field of the Invention
The present invention relates to a reclining device that includes an external teeth gear and an internal teeth gear and in which the rotation axis of one of the external teeth gear and the internal teeth gear revolves around the rotation axis of the other, the external teeth gear having external teeth on the outer circumferential surface thereof and being disposed with one of a member on the seat cushion side and a member on the seat back side, and the internal teeth gear having internal teeth of which the number of teeth is larger than that of the external teeth of the external teeth gear and that are configured so as to engage with the external teeth and being disposed with the other of the member on the seat cushion side and the member on the seat back side.
2. Description of the Related Art
One example of reclining devices that allow continuous adjustments is a reclining device that includes an external teeth gear and an internal teeth gear and in which the rotation axis of one of the external teeth gear and the internal teeth gear revolves around the rotation axis of the other, the external teeth gear having external teeth on the outer circumferential surface thereof and being disposed with one of a member on the seat cushion side and a member on the seat back side, and the internal teeth gear having internal teeth of which the number of teeth is larger than that of the external teeth of the external teeth gear and that are configured so as to engage with the external teeth and being disposed with the other of the member on the seat cushion side and the member on the seat back side.
The external teeth of the external teeth gear and the internal teeth of the internal teeth gear that are included in such a reclining device are shaped so as to be involute teeth, as shown in FIG. 13. To be more specific, as shown in the drawing, the plane, within the range B, of each of the external teeth 3 of the external teeth gear 1 that engages with the internal teeth 7 of the internal teeth gear 5 is convex and protrudes in the direction of the internal tooth 7. On the other hand, the plane, within the range A, of each of the internal teeth 7 of the internal teeth gear 5 that engages with the external teeth 3 of the external teeth gear 1 is concave and is recessed in the direction away from the external tooth 3 (For example, see Japanese Examined Patent Publication (Kokoku) No. H7-79740 (FIG. 3).